Microstructural evolution and sintering kinetics during spark plasma sintering of Fe and Al blended powder

The reaction diffusion between Fe and Al during spark plasma sintering (SPS) was studied. Microstructural evolution was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the sintering kinetics was disclosed. The main interphase of the SPS sample was Fe₂Al₅ at 773–873 K. Ball-milling enabled a large number of lattice defects and grain boundaries thus the reaction kinetics was accelerated, although the direct current can also promote those defects. After milling, the phase transformation kinetics was improved from 0.207 before mill to 4.56×10^?3. Besides, this work provided more details for the generation of Joule heating. The resistance offered to the electric path was considered to be the source of Joule heating, and particularly the resistance offered by the different contact interfaces of die, punch, graphite foil and the sample played a leading role for the generation of Joule heating during spark plasma sintering.     

真空烧结和氢致相变烧结制备Ti-xFe合金的组织演变过程和性能研究

以HDH-Ti粉和羰基Fe粉为原料,经冷等静压成形后,分别采用真空烧结和氢致相变烧结(HSPT)制备Ti-xFe合金(x=1%、5%、10%和15wt%),对比研究了两种烧结工艺中合金的密度、物相、组织演变过程和显微硬度等性能。结果表明：HSPT合金含有较多的孔隙,密度明显低于真空烧结合金的密度。两种方法制得合金中的β相含量均随Fe含量的增加而增加,且在HSPT制备的Ti-15Fe合金出现了TiFe中间相。HSPT合金制备过程中,H对Fe元素的扩散产生了显著的抑制作用。当Fe≥5%时,脱氢后在合金的β相内部析出短棒状或针状的次生α相,使得β相组织细小。当Fe≥10%时,Fe出现了明显的富集。同时H元素导致β相向粗大化的方向发展,而且随Fe含量的增加,β相粗化越明显。HSPT合金的显微硬度高于真空烧结合金,尤其是α相的显微硬度随Fe含量的增加而线性增大。     

Characterization of phase transformation and microstructure of nano hard phase Ti（C,N）-based cermet by spark plasma sintering

By means of optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM), the process of densification, the characterization of phase transformation and the microstructure for spark plasma sintering (SPS) nano hard phase Ti(C, N)-based cermet were investigated. It is found that the spark plasma sintering (SPS) enables the nano hard phase Ti(C,N)-based cermet to densify rapidly, however, the full densification of the sintered samples can not be obtained. The rate of phase transformation is significantly quick.When being sintered at 1 200℃ for 8 min, Mo2C is completely dissolved, and TiN dissolves into TiC entirely and disappears. Above 1200℃, Ti(C,N) begins to decompose and the atoms of C and N separate from Ti(C,N) resul-ting in the generation of N2 and the graphite. Due to the denitrification and the graphitization, the density and the hardness of sintered samples are rather low. The distribution of grain size of the sample sintered at 1350℃ covers a wide range of 90-500 nm, and most of the grain size are about 200 nm. The hard phase is not of typical core-rim structure. Oxides on the surface of particles can not be fully removed and present in sample as titanium oxide TiO2.Graphite exists in band-like shape.     

45钢表面电子束相变硬化过程中组织转变数值模拟

组织转变的模拟研究,对准确预测硬化处理后组织与残余应力的分布有重要意义。本研究建立了电子束扫描45钢表面相变硬化过程中温度场与组织转变的数学模型;模型中考虑了热源分布、热物性参数、热辐射等因素对温度场的影响,基于Scheil叠加法则考虑了快速加热对奥氏体开始转变温度的影响;计算了相变硬化过程中各相组织含量和空间分布;分析了快速加热对奥氏体转变的影响;并进行了相应试验验证。结果表明,完全相变硬化区马氏体体积分数高达92.5%;硬化层横截面马氏体分布呈月牙状,且组织过渡明显;相变硬化奥氏体开始转变温度可高达1246 K,完成转变时间可短至0.1 s;硬化区冷却过程只发生马氏体相变;模拟结果与实验结果吻合较好。     

Ti-1300合金等温时效过程中相结构和组织转变

采用OM、SEM、XRD和TEM等研究了固溶态Ti-1300合金在350~700℃等温时效过程中相结构和组织转变。结果表明,Ti-1300合金在350℃等温时效时,β相基体上开始弥散析出细小的颗粒状ω相,后期ω相消失,出现了片状的α相。亚稳β相的分解方式为:β→ω+β→α+β。在400℃等温时效1 h时,亚稳β相分离出了β′相,继续保温,β′相消失,出现了长针状α相,亚稳β相的分解方式为:β→β′+β→α+β。在500~700℃等温时效时,α相在β晶界和晶粒内亚晶界上快速形核,随着保温时间的延长,晶界α相逐渐向晶内生长为α集束,随着时效温度升高,α相的片层越厚;亚稳β相的分解方式为:β→α+β。     

烧结气氛对Ti(CN)基金属陶瓷组织和性能的影响

用X射线衍射、背散射扫描电镜及能谱仪等分析手段研究了烧结气氛(真空、N2、Ar)对不同成分TiC基和Ti(CN)基金属陶瓷合金显微组织和性能的影响.金属陶瓷在N2和Ar中烧结后,合金碳含量比在真空中烧结的碳含量低0.5%左右;在N2中烧结后,合金的氮含量提高了0.5%左右.环状结构心部可以是以钨等重金属元素为主要成分的碳化物,也可以是以钛为主要成分的碳化物和碳氮化物.环状结构为金属元素含量和分布不同的(Ti,W,Ta,Mo,Co,Ni)(C,N)固溶体,粘结相是与Ti,W,Ta,Mo,C,N等元素有不同溶解度的钴镍固溶体.真空烧结后组织结构比较均匀,合金的性能最好.在Ar、N2中烧结后,气氛中的氧和氮参加烧结反应,影响合金成分碳氮平衡,在合金表面形成壳层结构,产生表面缺陷,合金的密度、显微硬度、抗弯强度均有比较大的降低;N2气氛影响更大.     

热轧带状组织对冷轧双相钢组织性能的影响

研究了不同热轧卷取温度下带状组织的变化对冷轧连退双相钢组织性能的影响,分析了热轧组织的遗传性对连退后马氏体组织的影响,以及弥散分布的马氏体与连续分布的马氏体对成品力学性能的影响。结果表明,热轧卷取温度为550 ℃时,带状组织比其他卷取温度下的带状组织有所改善,得到的冷轧连退组织中的马氏体比较弥散,弥散分布的马氏体要比连续分布的马氏体具有更好的塑性指标。     

Effect of powder mixing process on the microstructure and thermal conductivity of Al/diamond composites fabricated by spark plasma sintering

Two powder mixing processes, mechanical mixing (MM) and mechanical alloying (MA), were used to prepare mixed Al/diamond powders, which were subsequently consolidated using spark plasma sintering (SPS) to produce bulk Al/diamond composites. The effects of the powder mixing process on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated. The results show that the powder mixing process can significantly affect the microstructure and the thermal conductivity of the composites. Agglomerations of the particles occurred in mixed powders using MM for 30 min, which led to high pore content and weak interfacial bonding in the composites and resulted in low relative density and low thermal conductivity for the composites. Mixed powders of homogeneous distribution of diamond particles could be obtained using MA for 10 min and MM for 2 h. The composite prepared through MA indicated a high relative density but low thermal conductivity due to its defects, such as damaged particles, Fe impurity, and local interfacial debonding, which were mainly introduced in the MA process. In contrast, the composite made by MM for 2 h demonstrated high relative density and an excellent thermal conductivity of 325 W·m-1·K-1, owing to its having few defects and strong interfacial bonding.     

热处理对高岭石结构转变及活性的影响

采用煅烧高岭石的方法制备矿物聚合材料,采用DTA-TG、XRD和IR分析等手段研究高岭石经过热处理后的结构转变过程。结果表明:热处理直接影响到高岭石结构转变及煅烧高岭石的活性。煅烧后,高岭石的结构转变经历了脱羟基(约541℃)、偏高岭石化(541～850℃)和Al2O3分凝(>950℃)3个过程,煅烧温度达到950℃后,生成新相γ-Al2O3。通过对煅烧高岭石所制备的矿物聚合材料抗折强度的评价确定了煅烧高岭石活性较适宜的热处理制度:煅烧温度为850℃,煅烧时间3 h。煅烧高岭石的长程无序特征是煅烧高岭石具有较高活性的原因,γ-Al2O3的生成是导致煅烧高岭石活性下降和矿物聚合材料抗折强度降低的主要原因。     

Nb和Mo对矿用磨球用钢微结构和相变的影响

对不同合金成分磨球用钢样品进行高温激光共聚焦显微镜(HT-CLSM)原位观察和JMatPro软件模拟计算,研究了Nb、Mo元素对其热处理过程中微结构和相变的影响。结果表明,试验钢中添加0.051%Nb元素的原奥氏体平均晶粒尺寸最小(38.8 μm),添加0.079%Mo元素的次之,无添加的最大,可达74.1 μm。添加Nb元素时,析出物类别主要为Nb(C, N)和MnS,析出物的数量最多,显著阻碍了高温奥氏体晶粒长大。添加Mo元素时,析出物类别主要为MnS和AlN,析出物数量次之,对奥氏体晶粒长大有一定的阻碍作用。Nb和Mo元素的添加均有利于扩大贝氏体转变区,增加贝氏体转变量,提高马氏体转变开始温度。     

Effect of VC addition on sinterability and microstructure of ultrafine Ti(C, N)-based cermets in spark plasma sintering

The effect of vanadium carbide (VC) addition on the sinterability and the microstructure of ultrafine Ti(C, N)-based cermets consolidated through spark plasma sintering (SPS) was systematically investigated using optical microscope, scanning electron microscope (SEM) with X-ray energy dispersive spectrometer (EDS), X-ray diffractometer (XRD) and transmission electron microscope (TEM). Our results reveal that the addition of VC increases the porosity of sintering body and depresses the sinterability of Ti(C, N)-based cermets. It is also found that the VC addition has a significant influence on the microstructure of ultrafine Ti(C, N)-based cermets, which inhibits the dissolution of titanium-containing compounds and the formation of inner rim phase and outer rim phase, thus preventing from grain growth. Owing to the depressed dissolution and precipitation, nitrogen liberation is mitigated, therefore resulting in less amount of graphite phase in the samples. In substance, VC changes the solubility of metallic elements in the binder, which makes more elements of Mo and W to be reserved in the binder and thus greatly decreases the content of titanium dissolved into the binder. The re-building solubility rule determines the development of phases and microstructure.     

相变温度及时间对SCM435钢盘条组织和性能的影响

针对小规格SCM435冷镦钢盘条因抗拉强度较高而影响后续加工的问题,设计了3种工艺,即通过调整终轧温度和斯太尔摩风冷线辊道速度,进而控制盘条相变温度和相变时间,使相变充分进行得到所需的铁素体+珠光体均匀组织,从而达到降低抗拉强度、提高面缩率的目的.试验结果表明,降低终轧温度至750℃、减小辊道速度至0.08 m/s,可...     

Y2O3掺杂ZrSiO4涂层的微观组织和相结构研究

本文采用大气等离子喷涂成功制备了ZrSiO4及Y2O3掺杂ZrSiO4涂层,研究了Y2O3掺杂后ZrSiO4涂层微观组织结构、力学性能,并研究了涂层在1300 ℃下的烧结行为。结果表明,等离子喷涂ZrSiO4涂层主要由ZrSiO4、t-ZrO2、少量的m-ZrO2及无定型SiO2组成,而等离子喷涂ZrSiO4-5%Y2O3涂层主要由c-ZrO2、少量ZrSiO4相及无定型SiO2组成。相较于ZrSiO4涂层,Y2O3掺杂略微提高了ZrSiO4-5%Y2O3涂层的硬度和断裂韧性。在1300 ℃高温烧结48 h后等离子喷涂ZrSiO4涂层中(t,m)-ZrO2和无定型SiO2反应生成重新ZrSiO4相,该反应伴随着体积收缩,使得涂层中存在着大量孔隙和裂纹。相较于纯ZrSiO4涂层, ZrSiO4-5%Y2O3涂层中主要是c-ZrO2相和ZrSiO4相,添加Y2O3有助于涂层中的ZrO2保持在立方相（c-ZrO2）,提高了ZrO2的高温相稳定性。     

控冷工艺对ER70S-6钢相变和组织的影响

通过热模拟机Gleeble - 15 0 0对控制冷却过程的模拟 ,研究了终轧温度、吐丝温度和相变区冷速对ER70S - 6焊丝钢相变点的影响规律 ,测定了该钢种的动态连续冷却转变 (CCT)曲线 ,研究了控冷工艺参数对组织结构、铁素体量和铁素体平均晶粒尺寸的影响 ,得出其影响规律性的结论。     

LPSO堆垛结构转变对挤压态Mg-2.0Zn-0.3Zr-5.8Y镁合金组织性能的影响

通过改变挤压温度以获得含有不同堆垛结构长周期相(LPSO)的Mg-2.0Zn-0.3Zr-5.8Y合金,研究LPSO相堆垛结构转变对挤压态合金组织性能的影响规律及其作用机制。结果表明:挤压温度为390℃,合金中有18R和14H 2种堆垛结构的LPSO相,其平均晶粒尺寸为(9.5±3.0)μm,合金的抗拉强度达到280 MPa,延伸率为18.7%;当变形温度达到420℃,合金中18R LPSO相全部转变为14H结构,平均晶粒尺寸大幅细化至(3.1±1.1)μm,合金的抗拉强度和延伸率均得到明显提高,分别达到330 MPa和20.8%;随着挤压温度的进一步提高,合金的平均晶粒尺寸逐渐变大,强度和延伸率开始逐渐降低。由于LPSO相堆垛结构转变和晶粒尺寸变化引起基面织构和柱面织构的强度发生变化,LPSO相形态改变以及晶粒细化是Mg-2.0Zn-0.3Zr-5.8Y挤压态合金室温力学性能变化的主要因素。     

焊接电流和药皮厚度对水下湿法焊接熔渣物相及微观组织的影响

文中采用自制的金红石型药皮焊条进行水下湿法焊接,重点分析了焊接电流和药皮厚度对熔渣物相及微观组织的影响.对熔渣的宏观形貌分析发现,当药皮厚度较薄时,焊后熔渣稀薄,覆盖不均匀,此外,焊接电流对焊接飞溅有重要影响,当焊接电流较大时,焊接过程中有大量飞溅产生.通过对熔渣的碱度系数及物相分析得出,熔渣的主要组成相为FeTiO₃和CaTiO₃,还有少量的MnTiO₃,FeF₃和Ca-Si-O相,药皮厚度和焊接电流对熔渣的碱度系数和组成相影响均较小.熔渣的微观组织分析发现,减小药皮厚度和增大焊接电流,熔渣中生成大量的树枝状组织,熔渣微观组织的方向性增强,有利于脱渣.     

Effect of Al content on the phase structure and the hydrogenation characteristic of La(Mg_(1-x)Al_x) alloys

1. Introduction Hydrogen-absorbing materials like sodium alanates, advanced BCC alloys, and Mg-based al- loys have been widely investigated [1]. Mg-based alloys are attractive as potential hydrogen storage materials because of their high storage capacity and low cost [2-3]. The hydrogen desorption kinetics has been improved using various methods [4-6], espe- cially alloying. It was reported that the kinetics of hydriding and dehydriding of Mg-based alloys can be improved by alloying with rar…     

Effect of AI content on the phase structure and the hydrogenation characteristic of La（Mg1-xAlx） alloys

La（Mg1-xAlx） （x=0.2, 0.4, 0.6, 0.8） alloys have been prepared using induction melting followed by annealing. It is found that partial substitution of Mg by Al does not lead to a change in crystal structure, and the alloys have a single LaMg phase when x 〈 0.4. The lattice parameter of the LaMg phase decreases obviously after the partial substitution of Mg by Al. However, further substitution of Mg by Al leads to the coexistence of multiple phases when x ≥ 0.6. The alloys consist of the LaMg, LaAl, LaAl2, and La5Al4 phases. The LaMg phase decreases, whereas the La5Al4 phase increases with the increase in x. The Al-substituted La（Mgo.6Al0.4） alloy can be hydrogenated into the tetragonal LaH3, cubic LaH3, MgH2, and LaPd under 5 MPa at 473 K for 5 d.     

铝热还原工艺条件对Al-Ti-Ce中间合金物相结构和合金元素浓度的影响

在Na3AlF6-NaCl-KCl氟氯混合电解质体系中,通过铝热还原法以TiO2和CeO2为Ti源和Ce源,制备Al-Ti-Ce中间合金。研究反应时间、反应温度、电解质构成（Na3AlF6质量百分含量）、K2TiF6添加量四种工艺条件对Al-Ti-Ce中间合金物相结构和合金元素浓度的影响。实验结果表明,在所有实验工艺参数范围内,制备的Al-Ti-Ce中间合金均由ɑ-Al、Al3Ti和Ti2Al20Ce三相构成。制备的最佳单因素工艺参数为：反应时间90 min,反应温度850℃,Na3AlF6质量百分含量40 %、K2TiF6添加量20 mol%。热力学分析结果从理论上进一步证明了在实验条件下几种主要化学反应的可行性。     

Effect of LiSbO3 on the phase structure, microstructure and electric properties of Sr0.53Ba0.47Nb2O6 ceramics

LiSbO₃ doped Sr_0.53Ba_0.47Nb₂O₆ ceramics were synthesized by conventional mixed-oxide method. The phase structure, microstructure, dielectric and ferroelectric properties of obtained ceramics were investigated. Pure tungsten bronze structure could be obtained in all ceramics and LiSbO₃ additive could promote densification and reduce the sintering temperature. The dielectric characteristics showed diffuse phase transition phenomena for all samples, which was proved by linear fitting of the modified Curie-Weiss law with γ value varying between 1.65 and 1.92. With increasing LiSbO₃ content, the transition temperature T_c decreased gradually to near room temperature. Normal ferroelectric hysteresis loops could be observed in all compositions, but the remnant polarization (P_r) and coercive field (E_c) all decreased gradually. Besides, the underlying mechanism for variations of the electrical properties caused by LiSbO₃ doping was explained in this work.